Blue-flame liquid-fuel burner process, apparatus and utilization systems

ABSTRACT

Blue-flame burner process, apparatus and utilization systems producing a quiet, stable, essentially sootless blue flame from liquid fuel, particularly hydrocarbon fuels, fuel oil and the like and producing substantially complete combustion of the fuel, being more efficient than conventional oil burners and eliminating particulate matter in the exhaust products, contributing to substantially reduced air pollution and additionally providing more efficient utilization of the heat generated. In the blue-flame process the kinetics of combustion are controlled by close and effective coupling to a heat sink, and novel close coupling systems with higher performance heat exchangers are provided. Compact, lightweight inexpensive burner units are provided which are adapted to be constructed with a generally rectangular J-shaped configuration adapted for close coupling to a planar area of a heat sink, if desired in certain embodiments; the rectangular configuration lends itself to convenient, inexpensive sheet metal construction suitable for large scale mass production techniques. The fuel nozzle, ignition device and damper controls are located at the base of the shorter leg of the J-shaped burner unit where they can be readily accessible for convenient adjustment to optimum settings during actual operation. The rectangular burner configuration is versatile for use in many different applications, environments and utilization systems as described, including applications similar to those which have heretofore been limited to gas burners and for modular arrangements of multiple burners stacked side-by-side for great heat release in a relatively compact volume. Multifuel burning capability is provided for interchangeably using fuel oil, kerosene or gasoline while achieving substantially the same desirable blue-flame characteristics in each case, suitable for mobile home applications, emergency heating, garages, use in remote locations, etc. A relatively cool fluepipe is achieved such that the conventional expensive brick or tile chimney can be eliminated.

United States Patent Bailey [15] 3,652,194 1451 Mar. 28, 1972 [54]BLUE-FLAME LIQUID-FUEL BURNER PROCESS, APPARATUS AND UTILIZATION SYSTEMSFrank W. Bailey, 663 Black Oak Ridge Road, Wayne, NJ. 07407 [22] Filed:Sept. 24, 1969 [2l] Appl.No.: 860,662

[72] Inventor:

521 u.s.c1 ..431/9,110/49,122/230, 431/116 51 Int.Cl ..F23m9/06 5sFieldofSearch ..43l/9,1l5,ll6;1l0/49; 122/230 56 References Cited U ITEDSTATES PATENTS 7 2,688,360 9/1954 Haynes et al.' ..431 115 3,078,914-2/1963 Bigelow ..431/115 FOREIGN PATENTS 0R APPLICATIONS 565,345 3/1958Belgium ..43 Ill l5 Primary Examiner-Edward G. Favors. Attorney Bryan,Parmelee, Johnson & Bollinger [57] ABSTRACT Blue-flame burner process,apparatus and utilization systems producing a quiet,.stable, essentiallysootless blue flame from liquid fuel, particularly hydrocarbon fuels,fuel oil and the like and producing substantially complete combustion ofthe fuel, being more efficient than conventional oil burners andeliminating particulate matter in the exhaust products, contributing tosubstantially reduced air pollution and additionally providing moreefficient utilization of the heat generated. In the blue-flame processthe kinetics of combustion are controlled by close and effectivecoupling to a .heat sink, and novel close coupling systems with higherperformance heat exchangers are provided. Compact, lightweightinexpensive burner units are provided which are adapted to beconstructed with a generally rectangular J-shaped configura-' tionadapted for close coupling to a planar area of a heat sink,

if desired in certain embodiments; the rectangular configuration lendsitself to convenient, inexpensive sheet metal construction suitable forlarge scale mass production techniques. The fuel nozzle, ignition deviceand damper controls are located at the base of the shorter leg of theJ-shaped burner unit where they can be readily accessible for convenientad- 7 justment to optimum settings during actual operation. The

rectangular burner configuration is versatile for use in many difierentapplications, environments and utilization systems as described,including applications similar to those which have heretofore beenlimited to gas burners and for modular arrangements of multiple burnersstacked side-by-side for great heat release in a relatively compactvolumev Multifuel burning capability is provided for interchangeablyusing fuel oil, kerosene or gasoline, while achieving substantially thesame desirable blue-flame characteristics in each case, suitable formobile home applications, emergency heating, garages, use in remotelocations, etc. A relatively cool fluepipe is achieved such that theconventional expensive brick or tile chimney can be eliminated.

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PATENTEDMAR28 1972 SHEET 8 BF 8 Y E m L RI E Z 5 3 TB R N. 0 W n K WN AA m BLUE-F LAME LIQUID-FUEL BURNER PROCESS, APPARATUS AND UTILIZATIONSYSTEMS DESCRIPTION The present invention relates to blue-flameliquid-fuel burner process, apparatus, and utilization systems forproducing a stable blue flame from liquid fuel, particularly hydrocarbonfuels, more particularly fuel oil and the like. The resulting blue flameis quiet and provides less excess air with complete, soot-freecombustion, thus, being more efficient than conventional yellow flameburners and eliminating particulate matter in the exhaust products. Theinvention provides means to advantageously control the flame temperatureby controlling the amount of recirculated gases and their degree ofcooling as they travel the recirculation path. The invention thusprovides substantially reduced air pollution, by eliminating particulatematter and minimizing oxides of nitrogen in the emission products and anumber of important operating advantages are provided in a wide varietyof utilization systems, as will be explained further below.

Conventional burners which have been in use prior to the presentinvention for burning liquid hydrocarbon fuels, fuel oil and the likeproduce yellow or yellowish-orange flames which are noisy, arecharacterized by incompletecombustion, and often deposit soot in theassociated heat exchanger surfaces, in theflue or chimney or dischargeparticulate matter into the atmosphere. Such yellow or yellow-orangeflames have the characteristic that any cool areas within the fireboxtend to quench and arrest the combustion in the localized regions of thecool areas, causing carbon precipitation and build-up of unburned carbonon them. The carbondeposits area fire hazard, impede heat transfer andreduce heat transfer efficiency. Such conventional combustion systemsare therefore not compatible with close coupled heat exchange devices.Prior fuel oil burners, in practice, involve a compromise betweenminimum excess air and smoke or soot conditions. Alteration in priorburner back pressure due to flue or heat exchanger blockage rapidlyreduces excess air and aggravates the smoke or soot conditions.

Among the advantages of the blue-flame liquid-fuel burner process,apparatus and utilization systems of the present invention are thoseresulting from the fact that they enable liquid hydrocarbon fuel, suchas fuel oil and the like, to be burned with a quiet, stable, efficientblue flame in which substantially complete combustion occurs with littleexcess air. The firebox and heat exchange surfaces remain cleaner thanwith conventional yellow flame burners, improved heat transfer isenabled to occur due to the use of cooler and highly connective heatexchange surfaces, and reduced maintenance and down time are achieved.The blue flame produced by utilizing this invention to burn fuel oil hasthe capability of a substantial dwell time in and about the firebox andheat exchange surfaces while substantially complete combustion occursand therefore can conveniently be utilized with cooperative advantage ina wide variety of efficient and effective utilization systems which aremore compact and less expensive than conventional fuel oil heatingsystems previously in use.

A summary of the features, aspects and advantages of the blue-flameliquid-fuel burner process, apparatus and utilization systems of thepresent invention includes the following:

1. in the blue flame process as provided by the invention, the flame hasits temperature controlled by the amount of recirculated gases and bythe degree of cooling of these gases provided by close coupling with aheat sink. The combustion box 40 provides the optimum temperature andresidence time to complete all chemical reactions and to allow theproducts therefrom to impinge on the heat sink. The kinetics ofcombustion are controlled by mixing of diluent gases at a temperatureoptimized by coupling to a heat sink.

2. The suction eductor system enables complete utilization of thecombustion volume 40. The combustion process stabilizes due torecirculation of combustible efflux from the mixing tube to a planeslightly downstream from the tertiary air ports. These factors allcooperate to provide complete combustion and to efficiently utilize theclose coupled, high pressure drop, cool heat exchanger surfacesdownstream from the combustion chamber.

3. A compact, light-weight bumerunit is provided, which is adapted to beconstructed with a generally rectangular configuration enabling closecoupling to a planar area of a heat sink.

4. The compact burner unit as disclosed has a J-shape with the fuelnozzle, ignition device and damper controls located at the base of theshorter leg of the J-shape where they can be readily accessible foradjustment to optimum settings during actual operation. l

5. The rectangular, J-shape burner lends itself to convenient,inexpensive sheet metal construction, suitable for large-scale massproduction techniques.

6. The process and apparatus are extremely versatile for use in manydifferent applications, and environments and utilization systems,including many of those which have heretofore been limited to gasburners.

7. A clean blue flame is produced substantially sootless, contributingto substantially reduced air pollution.

8. The noise level of the blue flame is lower than that for yellow flamecombustion. i

9. The process and blue-flame burner apparatus are reliable inoperation.

10. The J-shaped burner unit is easy to service. It is so compact andlight-weight that it can quickly and conveniently be removed andreplacedby another burner unit so that the original canbe returned tothe maintenance plant, thus providing centralized servicing usinginterchangeable, com,- pact mass-produced burner units.

11. The apparatus and fuel utilization systems shown are simple,reliable and low in cost. I

12. A multi-fuel burning capability is provided by the 'process andapparatus. Fuel oil, kerosene or gasoline may be used while providingsubstantially the same blue-flame characteristics, thereby beingconvenient for mobile home applications, garages, remote locations wherefuel availability is limited, for emergency heating, etc. It is notedthat the air atomizing nozzle 30 may also function as a gaseous fuelinjector without alteration of other components so that the combustionsystems as shown also have gas connection capability.

13. The rectangular'burner configuration which can be obtained lendsitself to modular arrangements of multiple burners for greatlyincreasing the over all heat release capacity in a relatively compactsystem.

14. Additional advantages in connection with the forced removal ofrelatively cool exhaust products are (a) reduced ignition pressurepulsations due to constant'induced pressure differential, i.e., theburner starts without a loud pressure pulse or hang because there is nosubstantial pressure build up during transient starting conditions; (b)simplified compact structures are achieved; and (c) a large pressuredifierential is provided across the heat exchanger.

15. The many novel aspects of the invention enable fuel oil and otherliquid fuels to be utilized more efficiently and more conveniently.

The various aspects, objects and advantages of the present inventionwill in part be pointed out and will in part become apparent from thefollowing description when considered in conjunction with theaccompanying drawings, in which:

FIG. 1 is a perspective view, with portions cut away to reveal theinterior, of a blue-flame liquid-fuel burning heater system embodyingthe present invention for heating hot water FIG 3 is a front elevationalview, as seen in the direction 3- 3 in FIG. 2, with the burner apparatusremoved to disclose the pair of openings into which it fits. Also, inFIG. 3 the top portion of the housingis shown cut away to reveal thecircular end of the cylindrical center-flue tank which contains thewater or other liquid to be heated.

FIG. 4 is a perspective view, with portions cut away to reveal theinterior, of another blue-flame liquid-fuel burning heater systemembodying the process of the present invention, the boiler being verycompact and having a single flowthrough conduit for heating water orother suitable liquid such as discussed above for similar purposes asabove.

FIG. 5 is a longitudinal and elevational sectional view of the heatersystem of FIG. 4.

FIG. 6 is a front sectional view, taken along the two portions of theline 6-6 in FIG. 5.

FIG. 7 is a sectional view of a blue-flame liquid-fuel burner having agenerally J-shaped configuration, including two leg portions and aninterconnecting back portion.

FIG. 8 is an end elevational view as seen looking in the direction 8-8in FIG. 7. T

FIG. 9 is an elevational view of the other end of the blueflame burnerof FIG. 7 as seen looking in the direction 9-9.

. FIG. 10 is a perspective view of a modular boiler system in whichmultiple blue-flame liquid-fuel burner units having generallyrectangular configuration are stacked together in generally spaced,parallel side-by-side arrangement, each associated with a smallrectangularboiler, thus providing large heat release capacity in arelatively compact volume;

FIG. 11 is a front elevational view of the modular boiler system of FIG.10; I

FIG. 12 is a perspective view of another modular boiler system similarto FIG. 10; and I FIG. "13 is a perspective view of a hot air heatingfurnace embodying the invention. Referring to FIGS. 1, 2 and 3 of thedrawings in greater detail, there is shown a blue-flame liquid-fuelburner heater system for heating hot water or other suitable liquid, asmentioned above. For convenience of reference the system 20 may bereferred to as a hot water heating system, but the reader is asked tonote that this system can be used to heat other suitable liquids withoutdeparting from the scope of the invention as claimed.

This heating system 20 produces a quiet, stable, efficient, blue flamewhen burning liquid hydrocarbon fuels and is well suited for burningfuel oil, kerosene or gasoline, interchangeably. In the followingdescription the particular fuel being burned is No. 2 fuel oil.

In this heating system 20 there is employed a vigorous forced ventingaction for removing the exhaust products. This forced venting isproduced by an eductor, as will be described further below. Therelatively cool exhaust gases can be removed through an uninsulatedflue. Other advantages of this forced venting are summarized above andwill be referred to further below. p v

The heating system 20 includes a blue-flame burner 22 having a generallyJ-shaped configuration including a first hollow leg section'24 whichserves as a mixing and preparation zone;

a second hollow leg section 26 which serves as a recirculation path, andan interconnecting hollow section 28 which joins the ends of the two legsections 24 and 26. The J-shaped configuration provides variousstructural and dynamic advantages. It allows structural support for therelatively short mixing tube 24, and it allows a hydrostatic balance inthe two leg sections 24 and 26 when adapted with a relatively highpressure drop heat exchanger having a vigorous eductor for the exhaustproducts. The pressure drop in the extended leg section 26 is relativelysmall and therefore avoids short circuiting of the combustion gases,i.e., avoids any reverse flow tendency through the mixing tube. Thus,the jet action of an air atomizing nozzle 30 is then capable ofmaintaining the proper flux of recirculating gases from the optimumpoint 106 in relation to the heat exchanger.

Liquid fuel is fed through a fuel line 29 and is atomized by the nozzle30, the atomized fuel being sprayed into the interior 32 of the firsthollow leg section 24. The particular fuel nozzle 30 shown is of the airatomization type, with air under pressure being supplied through an airline 34.

The region 32 within the hollow leg 24 serves as a fuel mixturepreparation zone, as will be explained in detail further below, and theend 36 of this hollow leg provides a discharge muzzle from which issuesa stable, quiet, efficient flue flame 38. The flame is directed into anelongated firebox 40 extending horizontally and having a rectangularparallelepiped configuration.

The bottom wall 42, side walls 44 and end wall 46 of the firebox 40 areconstructed of sheet metal, each of these sur-' faces being line by arectangular panel of stiff insulation board 48, such as glass fibermats, thus providing for inexpensive mass production. The upper surfaceof the firebox 40 is also lined by insulation 48 and includes'arelatively heavy metal plate 50 which serves as a heat sink in close andeffective heat exchange coupling with the hollow burner leg 26. In thisembodiment the burner leg 26 rests directly upon the heat sink plate 50in intimate face-to-face contact providing a large area 75 ofheat-conduction relationship therewith. I

Extending up from both longitudinal edges of the heat sink plate 50 areapair of housing side walls52 and 54 (FIG. 3) which effectively provide acradle at 55 for receiving a cylindrical center-flue heat exchange tank'56. This tank'56 is of a stock type such :as used in gas-fired hotwater heaters, except that in the System20 the tank 56 is orientedhorizontally in the cradle 55 with its concave end 57 at the left inFIG. 2 and its convex end 58 at the right.

In' this advantageous system 20, the hemicylindrical tank surface 59(FIG. 3) extending downwardly between the housing walls 52 and 54 plusthe concave end 57 plus the horizontal central flue 60, all serve asheat exchange surfaces for heating the liquid 62 within the tank 56.Therefore, as much heat as possible is extracted from the hot gases 64which flow from the firebox 40 upwardly through a port 66 into a firstheat exchange chamber 68 below the tank surface 59.

Between the concave tank end 57 and an end housing wall 70 and betweenportions of the side housing walls 52 and 54 is defined a second heatexchange chamber 72 (FIG. 2) which communicates with the first chamber68. A' third heat exchange chamber 74 is provided by the central tankpassage 60.

The interior surfaces of the first heat exchange chamber 68 are lined byinsulation material 48, except for the contact area 75 adjacent theburner leg 26 and except for the tank surface 59. The interior of thehousing wall 70 is insulated by material 48 as is also the interior ofthe hood 76 which connects the wall 70 with the lip 78 of the concavetank end 57.

A vigorous forced venting of the exhaust products is employed, asdiscussed above, which maintains all of the heat exchange chambers 68,72, 74 and the firebox 40 at sub-atmospheric pressure. The outlet end ofthe tank passage 60 is connected to a suction plenum chamber 80 having aVent uri throat 82 connected to an exhaust duct 84. A blower 86 has itsnozzle 88 directed up through the Venturi 82 for drawing the exhaustgases 90 up the duct 84. Alternativeforced venting means can beemployed, such as a blower wheel or fan in the flue 84, in lieu of theeductor 86, 88.

The liquid 62 to be heated is supplied through a pipe 92 extending downnear the cylindrical wall 59, and the hot liquid is withdrawn through apipe 94.

The heavy heat sink plate 50 is supported at its four corners by legs 96(FIG. 1 and a pair of cross braces 98 extend across beneath the firebox40.

The sub-atmospheric pressure in the firebox 40 causes secondary air tobe pulled in through a plurality of air intake apertures 100 surroundingthe nozzle 30. These apertures or ports 100 can be adjusted ineffectivearea by means of an adjustable rotatable damper disk having matchingopenings. This damper disk can be adjusted and locked in place by a setscrew, as will be understood. A spark plug 102 energized by an insulatedignition wire 104 serves to ignite the fuel.

Tertiary air may be drawn directly into the combustion volume 40 througha plurality of apertures 103 (FIG. 3) which are located near the burnerleg 24. These apertures or ports 103 can be adjusted in effective areaby means of slidable dampers having matching openings which are lockedin their adjusted positions by means of set screws.

In operation a minor proportion of the partially cooled hot gases 64 aredrawn into the intake end 106 of the hollow burner leg 26. Theserecirculated gases 108 (FIG. 2) are further cooled by substantial heatexchange in the elongated recirculation conduit provided by the interiorof the hollow burner leg 26. The withdrawn heat passes through the largearea of contact 75 into the heat sink plate 50, and the cooled gases 108pass through the interconnection passage 28 to enter the mixturepreparation zone 32.

In the zone 32 the cooled recirculated gases dilute the fuelair mixtureand allow the maintenance of a stable, blue-flame combustion process,thus providing a stable, quiet, efficient, soot-free blue flame 38. Itisnoted that there is a long effective residence time of the hot gasesin the four interconnected chambers 40, 68, 72, and 74 so that highlyeffective and efficient heat exchange occurs. I

The fuel nozzle 30, dampered air apertures 100 and ignition device 102are all conveniently accessible for adjustment during actual operationof the system 20. Moreover, the'J-shaped burner 22 can conveniently andsimply be withdrawn from the two openings 110 and 112, which accommodatethe burner legs 24 and 26, respectively, for removal and replacementservicing.

The heating system 120 shown in FIGS. 4, 5, and 6 is generally similarto the system described above, and corresponding reference numbers areused for the elements performing corresponding functions. The importantdifferences between the blue-flame heating system 120 and the system 20will be described. In lieu of the tank '56 and associated chambers andelements, there is a compact single flow-through conduit 122 having aplurality of radial longitudinal heat exchange fins 124 secured to it.The cold liquid inlet line 92 connects to one end of the flow-throughconduit 122 and the hot liquid outlet line 94 connects to the other end.It is noted that the liquid 62 (FIG. 5) passes through the conduit 122in a direction counter to -the flow of the hot gases 64 in advantageouscounter-current heat exchange relationship. An insulation blanket 126fills up the space within the top sheet metal housing 128 above the fins124, thus forcing all of the hot gases 64 to pass among these fins.

A small quartz glass observation window 130 (FIG. 5) may be located in aview port 132 at the back end of the firebox 40 for observing the blueflame 38.

The burner apparatus 22 is shown in greater detail in FIGS. 7, 8 and 9.It includes a conical baffle 140 which serves as a flame holder andinduces a thorough interrnixing of the cooled recirculated gases 108with the incoming fuel mixture 141 in the region 32. The adjustabledamper disk 142 and set screw 144 are shown. A mounting bracket 146 isshown, which may be attached to an external mounting bracket outside ofthe firebox 40. The spark plug 102 is preferably located above the levelof the air atomizing nozzle to avoid oil accumulation on the ceramicinsulator of the electrode in the spark plug.

An important advantage of the generally square burner leg section 24 isthat it provides four internal recirculation quadrants 137 into whicheddying vortices 139 are established for stabilizing the ignitionprocess and for improving the thorough mixing of the recirculated gases108 and the fresh incoming fuel-air mixture from the nozzle 30 and theair ports 100.

The modular heating system 160 shown in FIGS. 10 and 11 includes amultiplicity of the J-shaped burners 22 mounted in spaced, parallel,side-by-side relationship. The hollow recirculation leg 26 of eachburner 22 is secured to the lower surface of a small rectangular boilertank 162. Thus, the individual tanks 162 serve as heat sinks for coolingthe recirculated gases. The hot gases 64 pass upwardly between theparallel side surfaces of the multiple modular boilers 162 in good heatexchange relationship therewith. The spark plugs 102 are shown in analternate location below the level of the nozzles 30 to indicate theversatility of the burner. The preferred position is shown in FIGS. 1,2, 5 and 7. In practice the nozzle 30 and the spark plug 30 are mountedon a common mounting plate which is detachably secured to the burnerhead for mounting in either position as may be desired.

In this modular system 160 which has a common firebox 40 for all of theburners 22, a single spark plug ignitor may be employed, if desired,rather than having an ignitor for each burner.

In FIG. l2 is shown a modular heating system similar to that shown inFIG. 10 and. 11. The individual tanks 162 are interconnected by a waterinlet line 164 and a water outlet line In FIG. 13 is shown a hot airheating fumace 170. In the top portion of the furnace shell 172 is aheat exchanger 174 for heating hot air. A circulating air fan 176 of thecentrifugal blower type directs air to the lower surface of the base ofthe firebox 40. An extended length of rectangular pipe 26 is located incontact with the bottom of the firebox and is located beneath ahorizontal bafi'le 180 for directing the com-. bustion products in heatexchange relationship with the base of the firebox. A large rectangularoutlet 182 is provided for discharging the heated air from the heatexchanger 174.

The modular systems of FIGS. 10-13 are well adapted for high intensityradiant energy heat transfer from the walls defining the commoncombustion volume 40 to the surfaces of the heat exchangers 162 or 174.

In the embodiment of FIGS. 10-13, the exhaust products may be removed bythermogravity flow at moderate firing rates; whereas a forced pressuredifferential is used for higher firing rates.

What is claimed is:

l. A process for producing blue-flame combustion of liquid, hydrocarbonfuel comprising the steps of introducing a combustible mixture ofatomized liquid fuel and air into a mixing and preparation zone,igniting said combustible mixture and burning the fuel in a combustionvolume, recirculating combustion products from a region in thecombustion volume where the chemical reactions are substantiallycomplete, cooling the recirculated products by passing the recirculatingproducts in heat transfer relationship with a heat sink, returning aportion of the cooled recirculated gases to the combustion volume,thoroughly inter-mixing the returned portion of the cooled recirculatedgases with the fresh fuel air combustible mixture by commonly passingthem through said mixing zone, said mixing zone having a polygonalcross-sectional configuration, preferably square, providing for internalrecirculation quadrants, forming multiple internal recirculation pathsin said mixing zone quadrants by establishing eddying vortices therein,thereby diluting and cooling the mixture flowing through said mixingzone sufficiently to prevent the establishment of a flame front withinsaid mixing zone, said mixing zone being substantially shorter in lengththan the recirculation path, and discharging the cooled diluted ignitedmixture from the mixing zone thereby providing a stabilized combustiblemixture discharging from said mixing zone in blue-flame combustion inthe combustion volume.

2. A system for heating a fluid by blue-flame combustion of liquidhydrocarbon fuel comprising a heat exchanger, means for introducing thefluid into the heat exchanger and for removing the heated fluidtherefrom, means defining a combustion volume, conducting means defininga region for conducting combustion products from said combustion volumeinto heat exchange relationship with said heat exchanger, at least oneburner unit having a generally J-shaped configuration including a firstsubstantially open hollow leg section directed into said combustionvolume, injecting means for injecting atomized liquid fuel and airmixture into said first leg section, ignitor means for igniting thefuel-air mixture, a

' fuel-air mixture, a second hollow leg section for receiving a secondhollow leg section for receiving a portion of the com 1 and a hollowinterconnection section interconnecting one end of each of said legs forreturning the partially cooled combustion products from said second legto said first leg to be mixed with the fuel and air mixture, therebycontrolling the combustion kinetics in said combustion volume to produceblue-flame combustion in said volume.

3. A system as claimed in claim 2 in which a plurality of said burnerunits are positioned in spaced side-by-side relationship with theirrespective legs parallel with each other.

4. Apparatus forproducing blue-flame combustion with liquidfuelscomprising a burner unit having a generally J- shaped configurationincluding a first hollow leg section of generally square cross sectionserving as a mixing and preparatory zone, a second hollow leg sectionsewing as a recirculation path for combustion products, said firsthollow leg section being substantially shorter than said second hollowleg section, an interconnecting hollow section joining the ends of thetwo leg sections, and a vortex generating bafi'le means positioned inthe first hollow leg section near the juncture with said interconnectinghollow section. 5. Apparatus as claimed in claim 4 in which said vortexgenerating baffle means are provided by a downstream conveyent baffle.6. Apparatus as claimed in claim 5 in which said downstream conveyentbaffle has a conical configuration.

7. Apparatus for producing blue-flame combustion with liquid fuelscomprising a burner unit having a generally J- shaped configurationincluding a first hollow leg section serving as a mixing and preparatoryzone, a second hollow leg section serving as a recirculation path forcombustion products, an interconnecting hollow section joining theendsof the two leg sections, and an air atomizing nozzle associated withsaid interconnecting hollow section, said nozzle being directedtransversely of said interconnecting section into said first hollow legsection, said interconnecting hollow section and an inlet means nearsaid nozzle.

8. A system for heating a fluid by blue-flame combustion of liquidhydrocarbon fuel comprising at least one of heat exchanger means forintroducing the fluid into the heat exchanger and for removing theheated fluid therefrom,

means defining a combustion volume, conducting means defining a regionfor conducting combustion products from said combustion volume into heatexchange relationship with said heat exchanger, at least one burner unithaving a generally J-shaped configuration including a firstsubstantially open hollow leg section directed into said combustionvolume,

I injecting means for injecting atomized liquid fuel and air mixturesinto said first leg section, ignitor means for igniting the portion ofthe combustion products after they have passed in heat exchangerelationship with said heat exchanger, said second leg section beingcontained substantially within the conducting region and in close andeffective heat exchange contact with a heat sink, and a hollowinterconnection section interconnecting one end of each of said legs forreturning the partially cooledcombustion products to said first leg tobe- 10. A modular system for heating a fluid by blue-flame com- Ibustion of liquid hydrocarbon fuel comprising a plurality of heatexchangers including means for passing fluid therethrough, a combustionchamber, said combustion chamber including at least one ignitor meansfor igniting a fuel-air mixture, conducting means defining a region forconducting combustion products from said combustion chamber into heatexchange relationship with said heat exchanges, a plurality of J-shapedburner units mounted in spaced, parallel, side-by-side relationship insaid chamber, said burner units having a first substantially open hollowleg section directed into said combustion chamber, injecting means forinjecting atomized liquid fuel and air mixture into said first legsection; a second hollow leg section for receiving a portion of thecombustion products after they have passed in heat exchange relationshipwith saidheat exchangers, said second leg section being containedsubstantially within the conducting region and in close and effectiveheat exchange contact with a surface of one of said heat exchangers, anda hollow interconnection section interconnecting one end of each of saidlegs for' returning the partially cooled combustion products to said 1first leg to be mixed with the fueland air mixture, thereby controllingthe combustion kinetics in said combustion volume to produce blue-flamecombustion in said volume and providing high intensity radiant energyheat transfer from the combustion chamber to the heat exchange surface.

11. Apparatus for producing blue-flame combustion with liquid fuelscomprising a burner unit having a generally J- shaped configurationincluding a first substantially open shorter hollow leg section ofgenerally square cross section

2. A system for heating a fluid by blue-flame combustion of liquidhydrocarbon fuel comprising a heat exchanger, means for introducing thefluid into the heat exchanger and for removing the heated fluidtherefrom, means defining a combustion volume, conducting means defininga region for conducting combustion products from said combustion volumeinto heat exchange relationship with said heat exchanger, at least oneburner unit having a generally J-shaped configuration including a firstsubstantially open hollow leg section directed into said combustionvolume, injecting means for injecting atomized liquid fuel and airmixture into said first leg section, ignitor means for igniting thefuel-air mixture, a second hollow leg section for receiving a portion ofthe combustion products after they have passed in heat exchangerelationship with said heat exchanger, said second leg section beingcontained substantially within the conducting region and a hollowinterconnection section interconnecting one end of each of said legs forreturning the partially cooled combustion products from said second legto said first leg to be mixed with the fuel and air mixture, therebycontrolling the combustion kinetics in said combustion volume to produceblue-flame combustion in said volume.
 3. A system as claimed in claim 2in Which a plurality of said burner units are positioned in spacedside-by-side relationship with their respective legs parallel with eachother.
 4. Apparatus for producing blue-flame combustion with liquidfuels comprising a burner unit having a generally J-shaped configurationincluding a first hollow leg section of generally square cross sectionserving as a mixing and preparatory zone, a second hollow leg sectionserving as a recirculation path for combustion products, said firsthollow leg section being substantially shorter than said second hollowleg section, an interconnecting hollow section joining the ends of thetwo leg sections, and a vortex generating baffle means positioned in thefirst hollow leg section near the juncture with said interconnectinghollow section.
 5. Apparatus as claimed in claim 4 in which said vortexgenerating baffle means are provided by a downstream conveyent baffle.6. Apparatus as claimed in claim 5 in which said downstream conveyentbaffle has a conical configuration.
 7. Apparatus for producingblue-flame combustion with liquid fuels comprising a burner unit havinga generally J-shaped configuration including a first hollow leg sectionserving as a mixing and preparatory zone, a second hollow leg sectionserving as a recirculation path for combustion products, aninterconnecting hollow section joining the ends of the two leg sections,and an air atomizing nozzle associated with said interconnecting hollowsection, said nozzle being directed transversely of said interconnectingsection into said first hollow leg section, said interconnecting hollowsection and an inlet means near said nozzle.
 8. A system for heating afluid by blue-flame combustion of liquid hydrocarbon fuel comprising atleast one of heat exchanger means for introducing the fluid into theheat exchanger and for removing the heated fluid therefrom, meansdefining a combustion volume, conducting means defining a region forconducting combustion products from said combustion volume into heatexchange relationship with said heat exchanger, at least one burner unithaving a generally J-shaped configuration including a firstsubstantially open hollow leg section directed into said combustionvolume, injecting means for injecting atomized liquid fuel and airmixtures into said first leg section, ignitor means for igniting thefuel-air mixture, a second hollow leg section for receiving a portion ofthe combustion products after they have passed in heat exchangerelationship with said heat exchanger, said second leg section beingcontained substantially within the conducting region and in close andeffective heat exchange contact with a heat sink, and a hollowinterconnection section interconnecting one end of each of said legs forreturning the partially cooled combustion products to said first leg tobe mixed with the fuel and air mixture, thereby controlling thecombustion kinetics in said combustion volume to produce blue-flamecombustion in said volume.
 9. A system as claimed in claim 3 in which aplurality of said burners are positioned in spaced side-by-siderelationship with their respective legs parallel with each other inconjunction with a plurality of heat exchangers.
 10. A modular systemfor heating a fluid by blue-flame combustion of liquid hydrocarbon fuelcomprising a plurality of heat exchangers including means for passingfluid therethrough, a combustion chamber, said combustion chamberincluding at least one ignitor means for igniting a fuel-air mixture,conducting means defining a region for conducting combustion productsfrom said combustion chamber into heat exchange relationship with saidheat exchanges, a plurality of J-shaped burner units mounted in spaced,parallel, side-by-side relationship in said chamber, said burner unitshaving a first substantially open hollow leg section directed into saidcombustion chamber, injecting means for injecting atomized liquid fueland air mixture into said first leg section; a second hollow lEg sectionfor receiving a portion of the combustion products after they havepassed in heat exchange relationship with said heat exchangers, saidsecond leg section being contained substantially within the conductingregion and in close and effective heat exchange contact with a surfaceof one of said heat exchangers, and a hollow interconnection sectioninterconnecting one end of each of said legs for returning the partiallycooled combustion products to said first leg to be mixed with the fueland air mixture, thereby controlling the combustion kinetics in saidcombustion volume to produce blue-flame combustion in said volume andproviding high intensity radiant energy heat transfer from thecombustion chamber to the heat exchange surface.
 11. Apparatus forproducing blue-flame combustion with liquid fuels comprising a burnerunit having a generally J-shaped configuration including a firstsubstantially open shorter hollow leg section of generally square crosssection serving as a mixing and preparatory zone, a second openunobstructed longer hollow leg section of generally rectangular crosssection serving as a recirculation path for combustion products, and aninterconnecting hollow section joining the ends of the two leg sections.12. Apparatus as claimed in claim 11 in which the length of the firsthollow leg section is less than three and more than one times its width.